ATLANTA (CN) — The Georgia prosecutor investigating whether former President Donald Trump and his allies attempted to interfere with the state’s 2020 election results filed subpoenas Tuesday for U.S. Senator Lindsey Graham, former New York City Mayor Rudy Giuliani and others to testify before a special grand jury.

Fulton County Superior Court Judge Robert McBurney signed a “certificate of material witness” for Graham, Giuliani and others that says they have been deemed necessary to the investigation.

Launched in February 2021, the probe is focusing on a January 2021 phone call Trump made to the Georgia Secretary of State Brad Raffensperger asking him to “find” enough votes needed to overturn Joe Biden’s victory in the Peach State.

Fulton County District Attorney Fani Willis and her team are also looking into a phone call between Graham and Raffensperger in November 2020, the abrupt resignation of the U.S. attorney in Atlanta on Jan. 4, 2021, and comments made during December 2020 Georgia legislative committee hearings on the election.

Other attorneys and members of the Trump campaign being summoned include John Eastman, Cleta Mitchell, Kenneth Chesebro and Jenna Ellis as well as podcast host Jacki Pick Deason.

Over recent weeks, the 23-person special grand jury has heard testimony from an array of witnesses, including some who had direct contact with Trump and his associates.

Mitchell is being called as a witness for taking part in Trump’s infamous Jan. 2, 2021, call to Raffensperger. The conservative lawyer from Washington, D.C., claimed that more than 4,000 people who moved out of Georgia still voted in the state, but on the call Raffensperger’s general counsel Ryan Germany said that her data was incorrect.

Graham also made at least two phone calls to Raffernsperger and other members of his staff in the weeks after the November 2020 election, during which he asked about reexamining certain absentee ballots cast “to explore a more favorable outcome” for the former president.

According to the court filing, Giuliani, Deason and Ellis appeared publicly before the Georgia Senate in December 2020 in an effort to prove election fraud in multiple Georgia counties during the election.

They presented a video of election workers at the State Farm Arena in Atlanta that was purported to show them producing suitcases of unlawful ballots from unknown sources. The Georgia Secretary of State’s Office said its investigation into the incident revealed no evidence of voter fraud.

“There is evidence that the Witness’s appearance and testimony at the hearing was part of a multi-state, coordinated plan by the Trump Campaign to influence the results of the November 2020 election in Georgia and elsewhere,” McBurney wrote.

The judge said Eastman also contributed to spreading unfounded claims of voter fraud by advising lawmakers during the hearing that it was their “duty to replace the Democratic Party’s slate of presidential electors.”

The former law professor also pressed then-Vice President Mike Pence to block the certification of Biden’s Electoral College win and throw out the Democratic electors from seven swing states to keep Trump and the GOP in power.

Although he was largely shot down by a federal judge, Eastman argued for attorney-client protection when asked to provide evidence to the U.S. House committee investigating the Jan. 6 capitol attack. Giuliani, Mitchell, Chesebro and Ellis could also argue the same as prosecutors seek to secure their testimonies.

Chesebro, along with leaders of the Georgia Republican Party, coordinated a plan in which 16 people met at the Georgia State Capitol on Dec. 14, 2020, to cast purported Electoral College votes in favor of Trump.

Those summoned will be required to attend and testify before the special grand jury on July 12. Testimony could run through Aug. 31.

Raffensperger, several of his deputies and Georgia Attorney General Chris Carr have already testified before the grand jury. Governor Brian Kemp, who dismissed pressure from Trump to call a special session of the Legislature to reverse the election results, is also expected to provide a video statement later this month.

Last week, Willis sought to get testimony from Lieutenant Governor Geoff Duncan and former Senator William Ligon, who both argued that the Georgia Constitution shields them from testifying about their legislative-related activities. At a hearing on Friday, McBurney said that prosecutors will be unable to ask them any questions related to their conversations with other legislators.